Assaying, Microscopy, Mineralogy & XRF/XRD

Assaying, Microscopy, Mineralogy & XRF/XRD

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Assaying Lead-Zinc ore by XRS-FP. (2 replies and 3 comments)

L
Sohwohn
4 years ago
Sohwohn 4 years ago

Hello all! I am 28 years old. I lived in Hong Kong and visited China two months ago. I have a Bachelor's in Information Technology and I have never worked in this field until recently. I have been arranged to 'learn' assaying ore samples here. My father is working on several projects regarding tailings and some abandoned plants. Since I'm completely not familiar with this industry, my primary focus was to (sort of) master the use of the XRS machine. Throughout the 50 days I have spent here, I have learned the basics of XRS and starting to 'tune my own lines'. I'm by far satisfied with the learning progress, considering I'm receiving almost no help but only the online information through VPN with Google.

I have encountered an obstacle though that I could not find a solution for days. As peak of Zinc-Kb is 'blocking' the peaks of Pt-Ka and Au-Ka, and those of Pt-Kb and Au-Kb are unidentifiable. I want to remove Zn from the sample. I suspect Zn in the sample is in ZnO form (possibly ZnS but in my opinion unlikely). I have read a lot of articles about 'dissolving'(?) ZnO in HCl solvent or NaOH solvent. I have tried NaOH solvent and it should release hydrogen gas. It didn't give the 'pop' sound. The resulting solution (ZnO + NaOH) is warm. I haven't tried HCl yet.

I'm wondering, 1) if I can successfully dissolve ZnO in HCl solvent. Do I get Zn2+ ions? Or do I simply get ZnCl2? and 2) What I'm attempting to achieve is to ionize the ZnO and make ZnO dissolve in solution, then I would extract the ore sample (without Zn?) and use XRS to assay the sample again. Without ZnO, I should be able to see undisturbed peaks of Pt-Ka and Au-Ka.

I know I probably am not using proper English and chemical terms and it makes this difficult to read. Still, please help!

R
Richard S
4 years ago
Richard S 4 years ago

I think that you will get zinc chloride when you use hydrochloric acid on your material.  After filtering and rinsing you should be able to remove most of the interfering zinc for your analysis.

L
Sohwohn
4 years ago

Thank you very much for your reply! and Sorry for my late reply..!

Yes! I believe I asked the question because of that I have missed a big concept. which is that whether Zinc Chloride is soluble in water. Silly me..!

your reply 'rinsing' provided a keyword for me that I now 'wash out' the ions after some treatments, hopefully reducing some interfering elements. Thanks again for helping!

F
Siddiquf
4 years ago
Siddiquf 4 years ago

XRF works for a large number of elements but not for gold in exploration samples. As far as I know, the Lowest detection limit (LDL) for gold by XRF is ~10 ppm. So you will not see the Au Kα, even if you remove the zinc, unless your samples have >10 ppm gold. I am not sure about Pt detection. If you are not expecting >10 ppm gold in your samples, I suggest you switch to another method of analysis for gold, for example ICP-MS or similar. 

When vendors claim that their XRF analyzers can analyse gold, this claim is misleading; they are referring to determination of impurity elements in gold metal and not determination of gold in exploration samples. 

 

 

L
Sohwohn
4 years ago

Yes! you are right.

We usually remove the impurities first. For example, 500g ore particles reduced to 50g ore particles. If Au was not within the 450g of particles we got rid of, the conc. of Au in the 50g sample should have been increased.

Among last 3 weeks I (at least in my point of view) have progressed a lot. I have successfully gathered enough Au to see the beautiful clear peaks of Au and Pd. (Once Pd conc. in the particles was even high enough to reach 60%!) However, since our samples are particles, we cannot standardize the thickness and density, hence the resulting analysis can only be a rough 'reference'.

We hence got a furnace last week and we have been making Copper plates. Now we encountering a problem that we cannot vaporize some metal elements away (like Zn, Pb, Fe). Hence the interfering problem now exists again. We use 21g of Cu2O mixed with some other chemicals and 10g of ore particles. We have made standards of 1mg per unit of precious metals to make the XRS database (calibration). So roughly, 1mg/20g is 50ppm. Since we actually put 10g of ore particles into the furnace with 21g of Cu2O, if we read 1mg (relatively) Au in the final XRS it should indicate that the ore has at least around 100ppm Au. if the ore particle has only 50ppm and it makes us unable to see even 1mg peak in the XRS. We put the Copper plate into the furnace again with addition of another 10g of ore particles. This time if we read 1mg, it will then indicate that we have 50ppm of Au in the ore.

I'm not sure my English is well enough to elaborate my thoughts but this is the method we are trying to use for assaying. As I understand the best method to determine low-grade ore samples is maybe ICP or AAS, we don't have such equipment at this plant (but we do possess them in another plant) and somehow Ir and Rh are very very difficult to be dissolved but we value the existence of these elements.

Anyway, using copper plate (instead of the more commonly used Lead fire-assay) is one of the standard assaying methods that I have been told to study so that's what now I'm working on..

L
Sohwohn
4 years ago

What I'm thinking right now is to add some chemicals into the furnace so that the Zn Pd Fe compounds can be more easily vaporized. I'm reading some materials and have an idea but haven't tried yet.

This week I plan to work on Cyanidation mostly. We have a poison-free Cyanidation chemical and we have successfully used it to extract Pb from the vehicle TWC. Now we are trying to use it on ore particles to extract Au. Somehow it works but with unstable outcomes. I will be working on determining the factors associated in the process. Making reports and graphs or something like that.

Maybe next week I will be working on the assaying part again. 🙂

(here we have a small lab with limited equipment, and limited staffs. hence mostly me myself is the only one who puts effort working on these things such as researching and doing experiments with 'trial and error' method.... so the progress overall including assaying and process-planning is kind of very slow....)

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